Imaging optics, for example, optical microscopes have used very small, high quality objectives, usually lenses. These objectives require large ratios of diameter to focal length (called numerical aperture) in order to obtain high resolution. If the sample is a distance d away from an objective with diameter D, then the numerical aperture is given by:
      N    .    A    .    =      D                            4          ⁢                      d            2                          +                  D          2                    
At a wavelength λ, such an objective will be able to resolve details of size x, given by;
  x  =      λ          2      ⁢                          ⁢              N        .        A        .            
The lenses must also be made small, as the amount of spherical aberration (and chromatic aberration) in a lens increases with diameter. This means that the distance from the sample to the object must be small as well. In most cases, to further reduce the effect of spherical aberration, a combination of several custom designed lenses are used. It is impossible to manufacture a single element, large diameter, large numerical aperture lens which has no spherical aberration. For multi-element lenses the costs usually outweigh the benefits. In the case of reflecting objectives, the spherical aberration can be reduced more easily, but with the added complication that the sample will sit in front of the mirror and obscure the reflected light.
Another problem with high-power lenses is their small field of view. Parts of an object in the center of the field may be sharply imaged, but towards the edges of the image other aberrations are present which will degrade the quality of the image. To reduce the effect of these aberrations the distance from the sample to the object must be small along with the aperture. Again, it is impossible to manufacture a single element, large diameter, large numerical aperture lens which has no spherical aberration, let alone any useful field of view. In most cases, to reduce the effect of spherical aberration, a combination of several custom designed lenses are used. Multi-element lenses are very costly and even with the best objectives available, the working distance and useful field of view is small. Except for the design of specific multi-element objectives, there are no inexpensive methods for providing an increased field of view for a microscope. A wide field of view is simulated in most microscopes by quickly scanning the subject under a single, central point of high magnification.
Also, many schemes using holography for obtaining better microscopic images have been suggested. These include taking holograms of the object through a conventional microscope and then using the information contained in the hologram to produce large scale, aberration-free images of the object. This method relies on the use of a high quality microscope to begin with and, as such, has the usual problems associated with such methods including small working distance and expensive optical components. Other methods have corrected for the optics in a poor-quality microscope by holographic correction of the microscope optics, but these still require a second, high quality microscope for final viewing of the images. Both of these methods also suffer from the fact that the hologram is uniquely recorded for every sample, which is a problem when it comes to observing objects in real-time.
In the prior art is U.S. Pat. No. 5,426,521 to Chen et al (1995) which discloses correction of aberrations (which have to be first calculated) in an optical system by employing a liquid crystal panel which simulates a hologram from the calculations Also U.S. Pat. No. 5,657,168 to Maruyama et al (1997) discloses correcting aberration of an objective lens with an element having almost no power. However neither of these references discloses correcting aberrations in an optical system by use of a true hologram. And there is need and market for such aberration correction which permits relatively clear images to be obtained from flawed and thus low cost objectives.
There has now been discovered method and apparatus for correcting aberrations in an objective optical system that permits the use of relatively large and/or low cost objectives such as a lens or mirror, in which the imperfections thereof can be reduced or nullified to obtain an improved image of the object so viewed.